Transceiver devices are provided with variable gain amplifiers enabling gain adjustment. For example, a variable gain amplifier to amplify high-frequency signals received by an antenna is provided in a portable terminal for mobile communication. This variable gain amplifier amplifies received signals by a large gain when the received signals are weak, and amplifies received signals by a small gain, so that there is no output saturation, when the received signals are strong.
Further, a variable gain amplifier is provided in a portable terminal to amplify high-frequency signals to be transmitted from an antenna. This variable gain amplifier amplifies transmission signals by a large gain when the signals arriving at the base station are weak, and amplifies transmission signals by a small gain when the signals arriving at the base station are strong.
Such a variable gain amplifier has an emitter-grounded transistor which amplifies input signals, and a plurality of parallel cascode transistors (vertically stacked transistors) connected to the emitter-grounded transistor. Further, this variable gain amplifier has an output load connected to a portion of the plurality of cascode transistors, and a gate potential control circuit which performs on/off control of each of the cascode transistors.
By means of this gate potential control circuit, by controlling the fraction of current flowing to the output load among the input signal amplified by the emitter-grounded transistor (hereafter called the amplified signal), the gain (the intensity ratio of the output signal to the input signal) is adjusted. (For example, refer to Japanese Laid-Open Patent Publication No. 2007-259297.)